140 



scutal lateral portion, is smaller : it has a straight occludent margin, an excavated basal margin, 

 and a convex lateral margin. The middle portion shows near its base and at the scutal margin of 

 the valve two feebly developed rims, serving for the articulation of the valve with the fixed scutum. 

 The upper part of the whole valve is reflected, so that its outer surface is distinctly concave. 



The fixed scutum (PI. XI, fig. 6) is broader, but perhaps not quite so high as the 

 fixed tergum. Its shape is irregularly quadrangular, with the upper or occludent margin convex, 

 the rostral margin nearly straight, the long basal margin irregularly convex, according to 

 the surface of the object to which the shell is attached, the tergal margin is hollowed out 

 and furnished with a kind of radius and a rim along the basal portion of the margin, both 

 serving for the articulation with the fixed tergum. The outer surface of the valve shows distinct 

 ridges of growth, the direction of which, however, is rather irregular. From the slightly beaked 

 apex to the basi-rostral angle of the valve a feebly-undulating line divides the valve into two 

 triangular portions which together make a very blunt angle ; the whole valve is, moreover, not 

 flat but laterally bent towards the side of the moveable valves. 



The si ze of the shell as shown in the middle-sized specimen figured on PI. XII figs. 7 and 8 

 is 4.5 mm. height measured from the basal margin of the rostrum to the apex of the tergum; 

 3.5 mm. distance from apex of carina to that of the rostrum. These measurements are slightly 

 smaller in some of the other specimens. In the largest specimen of all, taken at Station 43, 

 the height measured 5.2 mm., the distance between the apex of rostrum and carina more than 4 mm. 



The study of the animal's body has given the following results: 



The body as a whole is much flattened, the prosoma is slender, the cirri rather long. 



Mouth laterally compressed, the anterior median line rounded but not bullate. Crest 

 of labrum with more than 20 small teeth on each side; pal pi elongately triangular, with the 

 inner margin slightly hollowed out, the outer margin convex and the tip bluntly pointed. A 

 row of short hairs is disposed along the inner margin, those at and near the extremity being 

 a little longer and curved. Over the outer surface a few shorter hairs are scattered. 



Mandible (PI. XIII, fig. 8) as usual: with three teeth and the inferior angle 

 terminating in a group of about 4 short spinelike, flattened teeth. The distance between the 

 extremities of teeth 1 and 2 little more than twice as long as that between teeth 2 and 3. 

 The first tooth long and pointed, teeth 2 and 3 shorter and not pointed at the extremity. 

 The upper margin of tooth 2 shows an indication of an accessory tooth, that of tooth 3 is 

 furnished with such an accessory tooth, and the upper or anterior margin of the inferior angle 

 with a row of 5 or 6 of such accessory teeth, of which the most inferior one is the longest 

 and stoutest. Inferior angle short, not produced. 



Maxilla (PI. XIII, fig. 9). Notch beneath the three upper spines hardly indicated, the 

 lower part, however, distinctly projecting forward. In the interspace between the three upper 

 spines and the projecting inferior part two spines are disposed. The inferior part bears half a 

 dozen stronger spines and a group of about 5 shorter and more delicate spines near the inferior angle. 



Outer maxillae with the inner face distinctly bilobed and numerous curved hairs 

 disposed along the outer margin and over part of the outer surface. 



Cirrus of the first pair situated very near the mouth with slightly unequal rami, both 



